1. Field of the Invention
The present invention relates to an apparatus and method for determining position information of a UE (User Equipment), and more particularly to an apparatus and method for transmitting GPS (Global Positioning System) auxiliary information over a broadcast channel needed to determine position information of the UE, selecting optimum GPS auxiliary information for every Node B, and transmitting the optimum GPS auxiliary information to individual Node Bs.
2. Description of the Related Art
There are a variety of methods for determining position information of a UE in a mobile communication network, and the following three position determinating methods have been developed and are described below as representative examples.
The first position determinating method determines position information of a UE (User Equipment) in cell units upon receiving information of a cell closest to the UE's position or information of the another cell managing the UE.
The second position determination method in a mobile communication network calculates either intensity information of a signal communicated between a Node B and a UE, a Time of Arrival (TOA) of the signal between the Node B and the UE, or a Time Difference of Arrival (TDOA) of the signal between a plurality of Node Bs and the UE, and triangulates the TOA or the TDOA in order to determine the position information of the UE.
The third position determination method determines position information of the UE using the Global Positioning System (GPS) developed by the US Department of Defense.
This method complements GPS techniques, and applies the complemented GPS techniques to a mobile communication network. This method is known as a Network Assisted GPS (NA-GPS) scheme. The NA-GPS scheme transmits GPS auxiliary information needed to determine the UE's position to the UE over a network (e.g., a mobile communication network), such that it shortens an initial position determination time of the UE.
FIG. 1 is a block diagram illustrating a conventional apparatus for determining position information of the UE. More specifically, FIG. 1 is a block diagram illustrating a position determinating device using the NA-GPS scheme. Referring to FIG. 1, the conventional position determinating device for the UE includes a UE (User Equipment) 110, a Node B 120, an RNC (Radio Network Controller) 130, an SMLC (Serving Mobile Location Center) 140, a Core Network (CN) 150, and a LSC (Location Service Client) client 160.
The Node B 120 transmits a propagation signal to the UE 110 positioned in a specific cell, measures a propagation signal received from the UE 110, and transmits predetermined data (e.g., TDOA, etc.) for determining position  information of the UE 110 to the RNC 130. In this case, a ‘Uu’ interface is adapted between the Node B 120 and the UE 110.
The RNC 130 manages radio resources of the Node B 120, controls a position determinating process of the UE, and calculates the UE's position. In this case, an ‘Iub’ interface is adapted between the RNC 130 and the Node B 120.
The SMLC 140 calculates and stores either TDOA auxiliary information or GPS auxiliary information associated with a specific cell, and transmits the GPS auxiliary information to the RNC 130 over an ‘Iupc’ interface.
The CN 150 manages information of one or more UEs 110, and performs a mobility management function, a session management function, and a call management function.
The LSC client 160 is connected to an external part of the network, and provides a service associated with the UEs' position information. The LSC client 160 requests UE position information from the CN 150, and transmits a position service to a corresponding UE using position information received from the CN 150. An ‘Iu’ interface is set up between CN 150 and RNC 130, while an ‘Le’ interface is set up between CN 150 and LSC client 160.
The GPS auxiliary information stored/managed in the SMLC 140 includes, among other things, satellite IDs, Almanac data, satellite orbital information, clock error correction values, ionospheric layer correction values, DGPS (Differential GPS) correction values of individual satellites, and list information of invisible satellites. The Almanac data is indicative of UE position information (e.g., model information) for every time interval in association with a predetermined time for detecting approximate UE position information. Specifically, the Almanac data has been adapted to discriminate visible satellites. The satellite orbital information and the clock error correction values are indicative of information for transmitting correct model information of a satellite location to the UE. The ionospheric layer correction values are adapted to correct an ionospheric layer delay error encountered during a propagation time in an ionospheric layer contained in a pseudo range between the satellite and the UE by about 50%, and is slowly changed as compared to other information. The DGPS correction values control deviation errors contained in a pseudo range using a reference Node B, and removes the deviation error, such that it can improve position accuracy of the UE. The Almanac data, the satellite orbital information, the clock error correction value, and the DGPS correction value must be determined for every satellite. 
The RNC 130 receives the GPS auxiliary information associated with a maximum of 12 satellites calculated by a reference GPS receiver positioned in the network from the UE 110 over the Node B 120 for managing a cell including the UE 110, such that it can calculate the UE's position. In this case, the GPS auxiliary information transmitted to the UE 110 has great magnitude.
In more detail, satellite orbital information and clock error information for every satellite requires 72 bytes, and the DGPS correction value requires data of 6 bytes. The Almanac data is acquired from 4 and 5 sub-frames of a GPS navigation message, and requires a single sub-frame for each satellite, such that the Almanac data and satellite health information are transmitted with all the satellite information, and 3 sub-frames are needed for satellite health and ionospheric layer error model information. Therefore, information denoted by “the number of satellites * 80 bytes” is required for transmission of all the information, and data of 15 bytes is required for other information. In conclusion, information equal to the length of (n*(72+6)+n*80+15) bytes must be transmitted to the UE to transmit GPS auxiliary information for calculating navigation data of N (or “n”) satellites to the UE. In this case, the minimum number of GPS satellites for determining a three-dimensional position is 4. Therefore, a minimum size required for transmission of GPS auxiliary information is denoted by 651(=(4*(72+6)+4*80+15)) bytes.
In order to satisfy the aforementioned requirements, the conventional system must sufficiently guarantee dedicated downlink data speeds for every UE to transmit the GPS auxiliary information to the UE.
If the UE requests position information from the network (e.g., a mobile communication network) to use a position-based service, a call bearer setup process for allocating a dedicated channel to the UE must be performed, such that an initialization time for determining the UE's position increases, and dedicated channels must be allocated to individual UEs requesting position information. Therefore, the amount of capacity and data traffic are linearly increased in proportion to the number of UEs.